Can someone recommend a red dot sight that will fit on a Sig P226 177 C02 pistol

i think your pounding a square peg in a round hole on this one 

you found a pistol that will take a LDC but there would no way to mount anything on the slide 

now you could get a under frame mount and mount it on that weaver-picatinny mount but there will be a problem

you will not know if the top rail will be centered over the slide 

oh i guess being off center might work but not for me 

something like this 

https://www.ebay.com/itm/Optics-20mm-Weaver-Picatinny-Rail-Mount-For-Airsoft-Pistol-Scope-Laser-Sight/192480524968?hash=item2cd0bbbaa8:g:CWsAAOSwNuxXX-MZ

but then it would have to clear the slide side 

so square peg in round hole 

Here is a mounting plate from ADE that should fit the rear sight notch on a Sig 226.

https://www.amazon.com/Ade-Advanced-Optics-Sigplate-1-Sightmark/dp/B06XNX2NQ8

Look also at their red dot sights.  Best price on red dots I have seen.

well if this was a real gun that mount might might work but you are not going be able to put weight on the slide 

being moving the slide back by a little puff of CO2 

I don't know anything about that gun, but looking at the picture, I think you might have better luck with a weaver mount laser.  My limited experience with laser sights has taught me that they can be quite accurate, but are VERY range-specific; IE the light goes in a straight line, but the pellet travels in a trajectory.

Like I said, if you take the time to dial in a laser sight at a specific distance, the pellet will go where the dot shines.  If you shoot at a fixed range, lasers can be really fun.  They are ideal for basement shooting.

https://www.ebay.com/itm/Universal-20mm-Picatinny-rail-red-dot-Mount-Base-for-glock-17-18-CNC-aluminum/114386338182?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D225080%26meid%3Df1df92e3738248529a80b9d8d386ef1b%26pid%3D100891%26rk%3D3%26rkt%3D6%26sd%3D201894536179%26itm%3D114386338182%26pmt%3D1%26noa%3D1%26pg%3D2332490%26algv%3DDefaultOrganic%26brand%3DUnbranded%2FGeneric&_trksid=p2332490.c100891.m5206

Not sure that will fit but it's aluminum!

https://m.aliexpress.com/wholesale/universal-picatinny-rail-mount-for-pistols.html